1. Field of the Invention
This invention relates to a group of compounds classified in the field or organic chemistry as 3-[4-(disubstituted amino)phenyl] or (9-julolidinyl)-3-(diphenylamino)phthalides useful in the art of carbonless duplicating as color formers in pressure-sensitive and thermal marking systems; to processes for the preparation thereof; and to pressure-sensitive duplicating systems and thermal marking systems containing the same.
2. Description of the Prior Art
Several classes of organic compounds of widely diverse structural types are known to be useful as color formers for carbonless duplicating systems. Among the more widely recognized classes, there may be named phenothiazines, for example, benzoyl leuco methylene blue; fluorans, for example, 2'-anilino-6'-diethylaminofluoran; phthalides, the class with which this invention is concerned, for example, crystal violet lactone; and various other types of color formers currently employed in commercially accepted carbonless duplicating systems. Typical of the many such systems taught in the prior art are those described in U.S. Pat. Nos. 2,712,507, 2,800,457 and 3,041,289 which issued July 5, 1955 and June 26, 1957 and June 26, 1962, respectively. Many of the color formers in the prior art suffer one or more disadvantages such as low tinctorial strength, poor light stability, low resistance to sublimation and low solubility in common organic solvents, the latter disadvantage thus requiring the use of specialized and expensive solvents in order to obtain microencapsulated solutions of sufficient concentration for use in pressure-sensitive copying systems.
The following appear to constitute the most relevant prior art relative to the present invention.
Japanese Patent Publication No. 71/4616 published Feb. 4, 1971 discloses a series of compounds having the formula ##STR1## wherein R.sub.1 is hydrogen or lower-alkyl; R.sub.2 is hydrogen, halogen or lower-alkyl; and R.sub.3 and R.sub.4 are each lower-alkyl. The compounds are prepared by reaction of a 2-[4'-(dialkylamino)benzoyl]benzoic acid with an appropriate aniline, and are stated to be useful as color formers in pressure-sensitive copying paper.
R. Valters and V. Tsiekure in Khim. Geterotsikl. Soedin. 1975, (11) 1476-8 discuss ring-chain tautomerism in 3-(N,N-diphenylamino)-3-phenylphthalide but disclose no utility for the compound.